Irritable bowel syndrome (IBS) is a functional disorder of the intestine characterized by altered bowel function (diarrhea, constipation, or both) and abdominal pain. It is the most common gastrointestinal disorder seen in general practice, and the prevalence of IBS has been estimated to be as high as 20% of the general population of North America. The majority of IBS sufferers are women, and women account for 80% of the cases of severe IBS.